Foil bearing supported motor with adjustable thrust bearing cap

ABSTRACT

An electric motor includes a stator; an annular end cap, fastened at a first end of the stator; a threaded seat that is mounted at an outward end face of the annular end cap for receiving a first gas foil thrust bearing; a shaft, inserted through the stator, through the annular end cap, and through the threaded seat; a thrust runner mounted at an end of said shaft adjacent the threaded seat; a first gas foil thrust bearing that is mounted into the threaded seat, adjacent a face of the thrust runner facing the stator; a bearing cap that has a threaded fitting by which it is attached onto the threaded seat; and a second gas foil thrust bearing that is mounted into the bearing cap adjacent to a face of the thrust runner opposite the first gas foil thrust bearing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC §119(e) of U.S.Provisional Application No. 62/174,088, filed Jun. 11, 2015 and isincorporated herein by reference.

BACKGROUND Technical Field

The invention relates to motor-driven equipment for movement of gasesthrough fuel cells. Particular embodiments of the invention relate tocentrifugal compressors.

Discussion of Art

All fuel cells require hydrogen, natural gas, process fluid/gas to theanode side to operate. Movement of gas is typically accomplished with ablower. Existing technologies that use conventional bearings (ballbearings and sleeve bearings) run at low speed and as a result will belarger and less efficient. In fuel cells the largest parasitic load inthe system is the air blower. Thus, any improvement in blower efficiencyhas a dramatic effect on the system overall efficiency. Additionally,these bearings often require oil lubrication that can contaminate thefuel cell and result in damage. Furthermore, in the process gas theremight be liquid or caustic material that might damage the motor stator.

SUMMARY OF INVENTION

Embodiments of the present invention preferably comprise the followingconfiguration and components and cooling methods.

The present invention is embodied in a single stage, centrifugalcompressor or blower, which has a rotating assembly that causes movementof gas through a compressor volute. The blower is mounted eithervertically or horizontally with mounting features like flanges that arepart of the volute. The blower may be hermetically sealed, and utilizesUL approved materials and fuel cell approved materials. The rotatingassembly of the blower comprises an impeller that is fitted onto theshaft on one end. The rotating assembly is supported by two gas foiljournal bearings, and by a set of gas foil thrust bearings. The bearingsare lubricated with a small amount of process gas that passes behind theimpeller and flows through the bearings and out the exit of the volute,if the cooling of the bearings warrants it. The rotating assembly isdriven by a motor. The motor laminations are shaped and formed ascooling fins on the outside of the machine, thus the motor can either beair cooled with the stator stack or have water hoses/pipes wrappedaround the fin features for water cooled. The windings are potted andcontain thermal conductive material and also are on the outside of themachine, so the environment around the machine self-cools the motor.Generally, the motor is powered by a Variable Frequency Drive. The motorstator has protective pieces on the ends of the motor stator and on theinner diameter of the stator which are bound together, either by spunweld or adhesive. The inner diameter protective sleeve, keeps theprocess gas from coming into contact with the inner diameter of themotor stator.

The blower does not have a motor housing; the cooling fins are part ofthe armature of the motor stator. Preferably, the armature is built upof laminations. For example, the laminations may include interleavedmaterials of relatively high or relatively low magnetic permittivity.

The present invention runs at high speed, thus the blower is smaller andweighs less than machines with comparable pressure rise and flow. Also,the blower has features that separates the process gas and leakage flowaway from the motor stator and allows the motor stator be cooled inanother fashion.

Moreover, certain embodiments of the invention incorporate a thrustbearing that is adjustable without disassembling the compressor. This isby contrast to conventional thrust bearings, which are shimmed to anon-adjustable position. According to these embodiments, a motor thrustbearing, which normally is needed to be adjusted with shims, instead isadjusted with a combination back cap and thrust cap screw that can setthe preload of the bearing either before test, during assembly, orduring testing.

Particular advantages of the present invention include the following:There is no possibility of oil contamination in the process gas sincethe machine is oil-free. The heat that is generated by the bearings ismoved into the process gas which is useful for energy savings. Theblower mounts easily on flanges which are part of the machine. Thecooling scheme allows the bearings and motor to run cooler which allowsthe machine to run faster. The cooling scheme reduces the number ofparts in the compressor, resulting in a lower manufacturing cost. Thereis not a motor housing for the stator or housing for the machine, whichsaves on the part count, protects the motor from process gas, andimproves cooling of the stator. Cooling fins are part of the motorstator laminations, which aid in the cooling of the machine. This alsoreduces part count and removes the thermal resistance that would occurif there were separate pieces. The protective end caps and inner sleeveon the stator, along with the potting material or encapsulant, protectsthe windings of the stator and the stator in general from contacting theprocess gas and damaging the stator. The motor has an adjustable thrustbearing cavity that can change the preload of the thrust bearing withoutthe need of shims, and can change the preload of the bearings while themachine is running. It is a more efficient assembly of the machine andreduces part count. It also removes constant assembly and disassembly ofmachines to “tune” the preload of the thrust bearings.

The varied exemplary embodiments of the invention, as briefly describedabove, are illustrated by certain of the following figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an isometric view of a blower according to an embodiment ofthe invention.

FIG. 2 shows a cross-sectional view of the blower of FIG. 1.

FIG. 3 shows an exploded (disassembled) perspective view of anadjustable bearing housing of the blower of FIG. 1.

FIG. 4 shows a cross-sectional view of the adjustable bearing housing ina large clearance condition.

FIG. 5 shows a schematic of a generic Fuel Cell System in which theinvention can be used.

FIG. 6 shows schematically a cooling scheme used in embodiments of theinvention.

FIG. 7 shows an isometric view of another blower according to anotherembodiment of the invention.

DETAILED DESCRIPTION

Embodiments of the invention are shown in the drawings and are describedas relating to a typical application of fuel cell fuel or air delivery(either stationary or mobile). Other applications of the invention,however, may include, for example: aeration units, printing systems, andair knives. The machine can be mounted in a vertical or horizontaldirection.

An isometric view of the blower 10 is shown in FIG. 1; FIG. 2 showsinternal parts of the blower 10 in a cross-sectional view. In certainembodiments, flanges 12 that connect to a customers system areintegrated into a volute 14 of the blower so as to reduce part numberand decrease leaks of the process gas. The volute 14 houses an impeller15, and supports a journal bearing sleeve 16, e.g., by way of capscrews. From the journal bearing sleeve 16 a motor, including a stator18, is supported by way of hollow rods 41. The volute also may house avaneless diffuser 19, through which the hollow rods 14 can be bolted;alternatively, the diffuser can be omitted.

Although shown as generally rectilinear or square in section, the stator18 equally may be round, ovoid, or of other shape convenient to itsoperation. The stator 18 includes an armature 20, which has fins 22, aswell as windings 24 that are wound through the armature. Outside theends of the armature 20, the windings 24 are encased in an encapsulantmaterial 26. End caps 38, 40 bracket the windings 24 and define a volumeof the encapsulant material 26. An adjustable bearing housing 48, whichincludes a combination journal and thrust bearing seat 50 and anadjustable bearing cap 52, is mounted to the end cap 40 at the end ofthe stator 18 that is opposite the volute 14.

Laminations of the motor stator 18 are layered along the longitudinalaxis of the stator to provide the armature 20, from which cooling fins22 protrude. Thus, the longitudinal cooling fins 22 protrude from anouter surface of the armature 20 and define longitudinal troughs on theouter surface. Shape and size of the stator fins 22 can be specifiedaccording to what the external and internal cooling analysis conditionsdetermine is needed. In certain embodiments the stator fins 22 may becircumferential, as shown in FIG. 7.

The stator windings 24 are wrapped through the armature in conventionalmanner, and outside the armature (where they protrude from the ends ofthe armature), they are potted in thermally conductive encapsulantmaterial 26. It is also possible to have an extra protective cap overthe potting material, but is not necessary. The encapsulant material 26seals the windings 24 to the armature 20, and serves as an outer housingof the stator. The encapsulant material 26 may have a thermalconductivity of no less than about 0.24 W/m-K and no more than about 166W/m-K; in certain embodiments, the encapsulant material 26 has a thermalconductivity of about 4.3 W/m-K. In addition to covering the windings24, the encapsulant material 26 also may cover substantially theentirety of the fins 22 to seal the entire outer surface of the armature20.

Optionally, coolant conduits (e.g. hoses or pipes containing a liquid,gaseous, or mixed-phase coolant) can be disposed in contact with thecooling fins 22, or can be run through the armature 20.

Thus, the electric motor stator 18 includes the armature 20 (formed bythe laminations) that surrounds a longitudinal opening 28 for receivinga shaft 30. The stator 18, which may be single phase or multi-phase,drives a motor rotor 32 that is integrally mounted into the shaft 30,which turns the impeller 15. The shaft 30 spins within two journalbearings 34, which are situated outside opposite ends of thelongitudinal opening 28. For example, as shown in FIG. 3, the journalbearings 34 can be seated within the journal bearing sleeve 16 and thebearing seat 50 that are adjacent to the protective stator end caps 38,40 as further discussed below.

Typically, the journal bearings are of the gas foil type. Accordingly,process gas will flow along the inner surfaces of the journal bearings34, both for lubricating the bearings and for cooling the motor rotor 32and stator 18. However, for electromechanical reasons the armature 20and windings 24 may be fabricated of or may include material that ischemically reactive with certain process gases. Accordingly, a(non-reactive) protective sleeve 36 lines the longitudinal opening 28and protects the armature 20 and the windings 24 from process gas.

To prevent direct contact of the process gas with the windings 24, theprotective inner diameter sleeve 36 is sealed, e.g. by spin welding oranother adhesion method, to protective end caps 38, 40 of the stator 18.The end caps 38, 40 and the protective sleeve 36 may consist of amaterial or materials that are chemically dissimilar to the armature 20and the windings 24. For example, the material or the materials of theend caps 38, 40 and of the protective sleeve 36 may be chemicallynon-reactive with the process gas to be passed along the longitudinalopening 28, whereas the armature 20 may be chemically reactive with theprocess gas. Thus, the end caps and the protective sleeve hermeticallyretain all the process gas to the inside of the machine, not allowingany to escape to the ambient environment. The end caps 38, 40 alsobracket and contain the windings 24 and the encapsulant material 26. Thejournal bearing sleeve 16 and the bearing seat 50 are sealingly mountedto their respective end caps 38, 40 such that there is a sealed path forprocess gas to flow from the volute 14 through the motor 18 and into theadjustable bearing housing 48.

Rigid tubing or hollow rods 41 are provided to clamp the motor statorlaminations between the protective endcaps 38, 40, and also can act ascoolant (air) conduits as discussed above. The tubing 41 also providesrigidity to the design by radially reinforcing the alignment of themotor stator 18 with the journal bearing sleeve 16 and bearing seat 50.The tubing 41 can be externally threaded to accept fasteners from thebearing seat 50, or can be internally threaded to accept bolts from thebacking plate 19 and from the bearing seat 50, thereby clamping togetherthe stator 18, the protective sleeve 36, and the end caps 38, 40. Inother embodiments, the tubing 41 can be smooth bore to accept bolts orstuds extending from the bearing sleeve 16 through the bearing seat 50or the other way. The tubing 41 may be sealed with the end caps 38, 40,e.g., by welding or by potting material 26. Thus, the tubing 41 supportsall the assembly pieces of the motor stator 18, essentially making thestator one piece. The rigid tubing 41 is not necessary for the design tooperate but helps with the durability of the design.

The shaft 30 extends beyond the protective end caps 38, 40 and has atits end proximate the end cap 40 a thrust runner 42, which is supportedby thrust bearings 44, 46. The thrust bearings 44, 46 are mounted onmating halves of a threaded (adjustable) bearing housing 48, whichincludes a threaded seat formed on the bearing seat 50 and carrying thefirst of the thrust bearings 44 as well as a threaded adjustable bearingcap 52 carrying the second of the thrust bearings 46. The threadedfeatures of the bearing seat 50 and of the bearing cap 52, which may bestraight threaded or taper (e.g., NPT) threaded, permit of adjusting thethrust bearing preload during operation of the blower 10.

The bearing seat 50 can be made integral with the end cap 40, or can bea separate component mounted onto the end cap 40 as shown in FIG. 3. Inaddition to an internal bore for receiving one of the journal bearings34, the bearing seat 50 also includes a land 54 for receiving the firstthrust bearing 44, as well as a threaded shoulder 56 that surrounds theland 54.

Referring also to FIGS. 3 and 4, the bearing cap 52 includes a land 58for receiving the second thrust bearing 46, as well as a threadedshoulder 60 that surrounds the land 58. On the land 58, an annulargroove 62 is indented. The groove 62 is provided for slidingly acceptingalignment pins 64 that extend from the bearing seat 50 through thethrust bearings 44, 46, thereby permitting threaded adjustment of thebearing preload by twisting the bearing cap 52, without torqueing eitherthe thrust bearings 44, 46 or the thrust runner 42. Additionally, theadjustable bearing cap 52 can include one or more features that allowfor easy adjustment, such as a knurled and/or easy grip feature, orwrench flats 66. The seat 50 and the bearing cap 52 can include, attheir peripheral surfaces, complementary visual features for indicatingan amount of preload or distance between the thrust cap land 58 to theopposite land of the seat 50, e.g. a Vernier scale 68.

As can be seen in FIG. 5, one application for the blower 10 is at theanode side of a fuel cell 200, i.e. as the fuel blower 210 in a fuelcell system. The fuel blower is a critical component in a fuel cellsystem, in which a process gas could be natural gas, hydrogen, oranother proprietary reactive gas. Furthermore, the blower would need acooling scheme whose internal cooling could not come out of the blower,but also would need the stator to be cooled and protected from theprocess gas.

FIG. 6 shows schematically a cooling scheme of the blower 10. Aninternal cooling scheme involves leakage of process gas from thecentrifugal compressor volute 14 through the first of the journalbearings 34, between the rotating assembly (shaft) 30 and the protectivesleeve 36 of the stator 18, through the second of the journal bearings34, then up and around the thrust runner and thrust bearings 42, 44, 46.The external cooling of the blower is shown through the motor statorfins 22, by conduction through stator and convection (forced and/ornatural) to the ambient environment by the means of the fins.

Thus, embodiments of the invention provide an electric motor, whichincludes a stator that surrounds a longitudinal opening for receiving ashaft; an annular end cap, fastened at a first end of the stator andsurrounding the longitudinal opening; and a threaded seat that ismounted at an outward end face of the annular end cap for receiving afirst gas foil thrust bearing, and that includes a through hole inregistry with the longitudinal opening of the stator. The threaded seatmay include a threaded annular shoulder surrounding a generally planarland for receiving the first gas foil thrust bearing. The electric motormay also include a shaft, inserted through the longitudinal opening ofthe stator, through the annular end cap, and through the through hole ofthe threaded seat, that includes a permanent magnet rotor formed in amiddle portion of said shaft and a thrust runner mounted at an end ofsaid shaft adjacent the threaded seat; and a first gas foil thrustbearing that is mounted into the threaded seat, adjacent a face of thethrust runner facing the stator. Further, the electric motor also mayinclude a bearing cap that has a threaded fitting by which it isattached onto the threaded seat; and a second gas foil thrust bearingthat is mounted into the bearing cap adjacent to a face of the thrustrunner opposite the first gas foil thrust bearing. The threaded seat maybe female or male threaded, with the threaded fitting beingcomplementary threaded. The bearing cap may include an annular grooveindented into a mounting surface radially inward of the threaded fittingand adjacent the second thrust bearing, in case the second thrustbearing has alignment pins that are seated slidingly into the annulargroove. The mounting surface (of the bearing cap) may be generallyplanar. The stator generally will include an armature surrounding alongitudinal opening for receiving the shaft, with fins protruding froman outer surface of said armature and providing cooling for the stator;and windings wound longitudinally through the armature. The stator mayalso include encapsulant sealing the windings to the armature, with theencapsulant filling a space between the armature and the annular end capand serving as an outer housing of the stator. The encapsulant also maycover substantially the entirety of the fins to seal the outer surfaceof the armature. The motor also may include a gas foil journal bearingmounted within the annular end cap for supporting a shaft to be receivedthrough the longitudinal opening. Additionally, the motor may include aprotective sleeve mounted within the stator adjacent the gas foiljournal bearing and sealingly connected with the annular end cap. Insuch case, the threaded seat may be sealingly mounted to the annular endcap such that a process gas flow path is established through theprotective sleeve, the journal bearing, and the end cap into thethreaded seat. Thus, in case the stator includes an armature, and asecond annular end cap, with the first and second annular end caps beingcoaxial and sealingly fitted at respective ends of the longitudinalopening; as well as a protective sleeve sealing an inward surface of thelongitudinal opening, and sealingly fitted to the through holes of thefirst and second end caps, then the end caps and the protective sleevemay consist of a material or materials that are chemically dissimilar tothe armature, so as to protect the armature from process gas that flowsthrough the motor along the shaft, within the longitudinal openingdefined by the end caps and the protective sleeve. For example, themotor also may include a shaft, inserted through the longitudinalopening of the stator, through the annular end cap, and through thethrough hole of the threaded seat, that includes a permanent magnetrotor formed in a middle portion of said shaft and a thrust runnermounted at an end of said shaft adjacent the threaded seat; an impellermounted at an end of the shaft adjacent the second annular end cap; afirst journal bearing mounted into the first end cap adjacent theprotective sleeve; and a second journal bearing mounted into the secondend cap adjacent the protective sleeve; such that the first end cap, theprotective sleeve, and the second end cap provide a flow path forprocess gas from the impeller through the motor to lubricate and coolthe journal bearings. Moreover, the motor may include a first gas foilthrust bearing that is mounted into the threaded seat, adjacent a faceof the thrust runner facing the stator; a bearing cap that has athreaded fitting by which it is attached onto the threaded seat; and asecond gas foil thrust bearing that is mounted into the bearing capadjacent to a face of the thrust runner opposite the first gas foilthrust bearing, such that the threaded seat is sealingly mounted ontothe first end cap, and the bearing cap is sealingly attached onto thethreaded seat, to provide that the flow path for process gas continuesinto the adjustable bearing housing that is formed by the threaded seatand the bearing cap.

Generally, embodiments of the invention support a method for adjustingpreload of a gas foil thrust bearing, which includes mounting thebearing into a threaded seat; sealingly attaching a threaded cap ontothe threaded seat, with a surface of the threaded cap in axial registryto the bearing; and threading the threaded cap toward or away from thebearing to adjust the preload.

Although exemplary embodiments of the invention have been described withreference to attached drawings, those skilled in the art neverthelesswill apprehend variations in form or detail that are consistent with thescope of the invention as defined by the appended clauses.

What is claimed is:
 1. An electric motor comprising: a stator thatsurrounds a longitudinal opening for receiving a shaft; an annular endcap, fastened at a first end of the stator and surrounding thelongitudinal opening; and a threaded seat that is mounted at an outwardend face of the annular end cap for receiving a first gas foil thrustbearing, and that includes a through hole in registry with thelongitudinal opening of the stator.
 2. The electric motor as claimed inclaim 1, wherein the threaded seat includes a threaded annular shouldersurrounding a generally planar land for receiving the first gas foilthrust bearing.
 3. The electric motor as claimed in claim 1, furthercomprising: a shaft, inserted through the longitudinal opening of thestator, through the annular end cap, and through the through hole of thethreaded seat, that includes a permanent magnet rotor formed in a middleportion of said shaft and a thrust runner mounted at an end of saidshaft adjacent the threaded seat; and a first gas foil thrust bearingthat is mounted into the threaded seat, adjacent a face of the thrustrunner facing the stator.
 4. The electric motor as claimed in claim 3,further comprising: a bearing cap that has a threaded fitting by whichit is attached onto the threaded seat; and a second gas foil thrustbearing that is mounted into the bearing cap adjacent to a face of thethrust runner opposite the first gas foil thrust bearing.
 5. Theelectric motor as claimed in claim 4, wherein the threaded seat isfemale threaded and the threaded fitting is male threaded.
 6. Theelectric motor as claimed in claim 1, wherein the bearing cap includesan annular groove indented into a mounting surface radially inward ofthe threaded fitting and adjacent the second thrust bearing, and thesecond thrust bearing has alignment pins that are seated slidingly intothe annular groove.
 7. The electric motor as claimed in claim 6, whereinthe mounting surface is generally planar.
 8. The electric motor asclaimed in claim 1, wherein the stator further comprises: an armaturesurrounding a longitudinal opening for receiving the shaft, with finsprotruding from an outer surface of said armature and providing coolingfor the stator; and windings wound longitudinally through the armature.9. The electric motor as claimed in claim 8, further comprisingencapsulant sealing the windings to the armature, wherein saidencapsulant fills a space between the armature and the annular end capand serves as an outer housing of the stator.
 10. The electric motor asclaimed in claim 9, wherein the encapsulant also covers substantiallythe entirety of the fins to seal the outer surface of the armature. 11.The electric motor as claimed in claim 1, further comprising a gas foiljournal bearing mounted within the annular end cap for supporting ashaft to be received through the longitudinal opening.
 12. The electricmotor as claimed in claim 11, further comprising a protective sleevemounted within the stator adjacent the gas foil journal bearing andsealingly connected with the annular end cap.
 13. The electric motor asclaimed in claim 12, wherein the threaded seat is sealingly mounted tothe annular end cap such that a process gas flow path is establishedthrough the protective sleeve, the journal bearing, and the end cap intothe threaded seat.
 14. The electric motor as claimed in claim 1, whereinthe stator further comprises: an armature surrounding a longitudinalopening for receiving the shaft, with fins protruding from an outersurface of said armature; a second annular end cap, wherein the firstand second annular end caps are coaxial and are sealingly fitted atrespective ends of the longitudinal opening; and a protective sleevesealing an inward surface of the longitudinal opening, and sealinglyfitted to the through holes of the first and second end caps, whereinthe end caps and the protective sleeve consist of a material ormaterials that are chemically dissimilar to the armature.
 15. Theelectric motor as claimed in claim 15, further comprising: a shaft,inserted through the longitudinal opening of the stator, through theannular end cap, and through the through hole of the threaded seat, thatincludes a permanent magnet rotor formed in a middle portion of saidshaft and a thrust runner mounted at an end of said shaft adjacent thethreaded seat; an impeller mounted at an end of the shaft adjacent thesecond annular end cap; a first journal bearing mounted into the firstend cap adjacent the protective sleeve; and a second journal bearingmounted into the second end cap adjacent the protective sleeve; whereinthe first end cap, the protective sleeve, and the second end cap providea flow path for process gas from the impeller through the motor.
 16. Theelectric motor as claimed in claim 16, further comprising: a first gasfoil thrust bearing that is mounted into the threaded seat, adjacent aface of the thrust runner facing the stator; a bearing cap that has athreaded fitting by which it is attached onto the threaded seat; and asecond gas foil thrust bearing that is mounted into the bearing capadjacent to a face of the thrust runner opposite the first gas foilthrust bearing, wherein the threaded seat is sealingly mounted onto thefirst end cap, and the bearing cap is sealingly attached onto thethreaded seat, wherein the flow path for process gas continues into theadjustable bearing housing that is formed by the threaded seat and thebearing cap.
 17. The electric motor as claimed in claim 17, wherein thebearing cap includes an annular groove indented into a mounting surfaceradially inward of the threaded fitting and adjacent the second thrustbearing, and the second thrust bearing has alignment pins that areseated slidingly into the annular groove.
 18. The electric motor asclaimed in claim 18, wherein the mounting surface is generally planar.19. A method for adjusting preload of a gas foil thrust bearing,comprising: mounting said bearing into a threaded seat; sealinglyattaching a threaded cap onto the threaded seat, with a surface of thethreaded cap in axial registry to said bearing; and threading thethreaded cap toward or away from said bearing to adjust said preload.